This rule was added in rubocop-rspec 2.9.0.
We were using `be_nil` 50% of the time, and `be nil` the rest of the
time. No strong preference for either one, but IMHO we don't lose
anything be being consistent.
This way we can simplify the code and don't have to rely on `.try`
statements which are confusing and so we don't allow them in the
`Rails/SafeNavigation` Rubocop rule.
